Electric cartridge fuses with blown fuse indicator

ABSTRACT

A cartridge fuse provided with a blown fuse indicator arranged in coaxial relation with the casing of the fuse and forming an integral part of the fuse. The blown fuse indicator includes an indicator housing arranged in coaxial relation to the casing of the fuse and defining a shoulder abutting against the end surface of one of the pair of terminal caps by which the casing of the fuse is closed. The indicator housing has a sleeve-like extension overlapping the lateral surface of one of said pair of terminal caps and affixed to said one of said pair of terminal caps.

United States Patent Kozacka [451 May 16, 1972 [54] ELECTRIC CARTRIDGE FUSES WITH BLOWN FUSE INDICATOR [72] Inventor: Frederick J. Kozacka, South Hampton,

[73] Assignee: The Chase-Shawmut Company, Newburyport, Mass.

[22] Filed: Dec. 15, 1970 [21] Appl. No.1 98,423

3,179,774 4/1965 Swain ..337/244 FOREIGN PATENTS OR APPLICATIONS 701,4l5 12/1953 Great Britain ..337/244 Primary Examiner-Bernard A. Gilheany Assistant ExaminerDewitt M. Morgan Attorney-Erwin Salzer [57] ABSTRACT A cartridge fuse provided with a blown fuse indicator arranged in coaxial relation with the casing of the fuse and forming an integral part of the fuse. The blown fuse indicator includes an indicator housing arranged in coaxial relation to the casing of the fuse and defining a shoulder abutting against the end surface of one of the pair of terminal caps by which the casing of the fuse is closed. The indicator housing has a sleevelike extension overlapping the lateral surface of one of said pair of terminal caps and affixed to said one of said pair of terminal caps.

3 Claims, 3 Drawing Figures ELECTRIC CARTRIDGE FUSES WITH BLOWN FUSE INDICATOR BACKGROUND OF INVENTION Cartridge fuses for relatively small current ratings include a tubular casing of insulating material and a pair of terminal caps are mounted on the ends of the casing and close the latter. If such a fuse is intended to be provided with a blown fuse indicator the latter is generally arranged in coaxial relation to the casing of the fuse outside of the space bounded by the terminal caps of the fuse and affixed to the fuse insuch a way as to form an integral part thereof so that the fuse and its indicator jointly form a structural unit. There are a number of prior art methods to achieve these ends, but none of them is entirely satisfactory. The present invention relates to an improved fuse and blown fuse indicator unit of the above description.

SUMMARY OF THE INVENTION An electric cartridge fuse embodying this invention includes a tubular casing of insulating material and a pair of terminal caps mounted on the ends of said casing and closing its ends. A ribbon fuse link interconnects conductively said pair of terminal caps. There is a pulverulent arc-quenching filler inside the casing which embeds the ribbon fuse link. A blown fuse indicator restraining wire extends across the end surface of one of said pair of terminal caps to the outside of said casing. A tubular blown fuse indicator housing arranged in coaxial relation to said casing defines a shoulder abutting against said end surface of said one of said pair of terminal caps. Said blown fuse indicator housing further has a sleeve-like extension engaging and overlapping the lateral surface of said one of said pair of terminal caps and affixed to said one of said pair of terminal caps. There is a blown fuse indicator inside of the indicator housing. The former includes a pair of coaxial complementary indicator caps biased in opposite directions by a helical spring arranged inside said pair of indicator caps, and means for securing one of said pair of indicator caps to the end of said blown fuse indicator restraining wire extending across said end surface of said one of said pair of terminal caps.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevation of a fuse embodying the present invention;

FIG. 2 is a longitudinal'section of the fuse shown in FIG. 1 taken along 2-2 of FIG. 1; and

FIG. 3 is a transverse section of the structure of FIGS. I and 2 taken along 33 of FIG. 2 and drawn on a larger scale than F IG.2.

DESCRIPTION OF PREFERRED EMBODIMENT In the drawings numeral 1 has been applied to indicate a tubular casing of insulating material closed by a pair of terminal caps 2 mounted on the ends of casing l and closing thelatter. Casing I is provided with a pair of grooves and the axially inner ends 2' of caps 2 are rolled into these grooves to firmly secure caps 2 to casing I. As seen in FIGS. 1 and 2 an additional terminal cap 3 is mounted on the right terminal cap 2. The axially inner end 3 of cap 3 is crimped radially inwardly to secure it firmly to the terminal cap 2 on which terminal cap 3 is mounted. Ribbon fuse link 4 interconnects conductively terminal caps 2 and 2,3. Ribbon fuse link 4 is arranged in a plane of symmetry of casing l, and is provided with four serially arranged points of reduced cross-sectional area, or necks 4'. Two of necks 4' are sandwiched between insulating plates 5 to control the arc voltage generated by the fuse incident to blowing thereof under major fault current conditions. Reference may be had to US. Pat. No. 2,964,604 to RC. Jacobs. Jr. et al., Dec. 13, I960 for CURRENT-LIMITING FUSE HAVING COMPOUND ARC-VOLTAGE GENERAT- ING MEANS for further details as to the structure of plates 5 and their mode of operation. An overlay 6 of tin, or other low fusing point link severing metal is arranged near the neck 4 at the center of the fuse link 4. The fuse link is preferably of silver, and is embedded in a pulverulent arc-quenching filler 7 inside of easing 1. Filler 7 is preferably quartz sand. The end surfaces of terminal caps 2 form recesses in the shape of truncated cones and the axially outer ends of ribbon fuse link 4 project through slots 2" in the end surfaces of caps 2 into the aforementioned recesses. Each of these recesses is filled with a body of solder conductively connecting the axially outer ends of fuse link 4 to terminal caps 2. Casing 1 further houses an indicator restraining wire 9 arranged parallel to, and in close proximity to, the axis of casing l and substantially within the plane defined by ribbon fuse link 4. Restraining wire 9 extends across the end surfaces of the left terminal cap 2, and the right end of restraining wire 9 is firmly clamped between the lateral surface of right terminal cap 2, and the lateral surface of the outer terminal cap 3. Reference numeral 10 has been applied to indicate a tubular blown fuse indicator arranged in coaxial relation to casing l and defining a shoulder 10' abutting against the end surface of left terminal cap 2. Indicator housing 10 has a sleeve-like extension 10'' engaging and overlappingthe lateral surface of left terminal cap 2, and affixed to that terminal cap. To this end the axially inner end of extension 10" is crimped radially inwardly, as shown at 10". A blown fuse indicator is arranged inside of indicator housing 10. The former includes a pair of coaxial complementary indicator caps 11 and I2 biased in opposite direction by a helical spring 13 arranged inside of caps 11,12. Indicator cap or indicating 12 is secured by means of pin or tie rod 14 to the end of restraining wire 9 extending across the end surface of left terminal cap 2. The right end of pin or tie rod I4 is flat, and perforated, and wire 9 is threaded through the perforation in tie rod 14. The left end of tie rod 14 projects through the end surface of cap 12 and is upset as indicated at 14'.

On occurrence of an overload of inadmissible duration overlay 6 melts and this severs fuse link 4 at the adjacent neck 4' by a metallurgical reaction between the overlay metal and the metal of which the fuse link proper is made, e.g. silver. This, in turn, causes kindling of an electric are at the point of break. On account of the proximity between restraining wire 9 and the point of break in fuse link 4 the heat of the are kindled at the point of break of fuse link 4 severs restraining wire 9. This allows cap 12 to move under the action of spring 13 from its'normal position shown, to its indicating position, i.e. to move from right to left as seen in FIG.2. In the indicating position cap 12 is outside of housing 10 and the enlarged or flattened end of rod 14 abuts against cap 13.

On occurrence of major fault currents ribbon fuse link 4 fuses simultaneously at its five necks 4. The necks 4 not covered by plates 5 are sufficiently close to restraining wire 9 to cause the latter to be severed by the heat of each are kindled at each point of break formed by a non-plate-covered neck 4'. As a result, indicator cap 12 is free to be propelled from right to left by the action of helical spring 13.

In some instances it may be desirable to arrange the restraining wire 9 not in sufficiently close proximity to ribbon link 4 to cause the former to be severed by the heat of the are which takes the place of ribbon link 4 when the fuse blows. When the current path through fuse link 4 is interrupted a voltage appears across restraining wire 9 and the following current path including wire 9 is established: housing 10, caps 13 and I2, rod l4, wire 9, cap 3. Therefore the wire 9 is destroyed by current flow through it, should it not have been destroyed previously by the heat of the are which takes the place of ribbon fuse link 4.

I claim as my invention:

1. An electric fuse including a. a tubular casing of insulating material;

b. a pair of terminal caps mounted on the ends of said casing and closing the ends thereof;

c. a ribbon fuse link conductively interconnecting said pair of terminal caps;

d. a pulverulent arc-quenching filler inside said casing embedding said ribbon fuse link;

e. a blown fuse indicator restraining wire extending across the end surface of one of said pair of terminal caps to the outside of said casing;

f. a tubular blown fuse indicator housing arranged in coaxial relation to said casing and defining a shoulder abutting against said end surface of said one of said pair of terminal caps, said blown fuse indicator housing further having a sleeve-like extension engaging and overlapping the lateral surface of said one of said pair of terminal caps and affixed to said one of said pair of terminal caps; and

g. a blown fuse indicator inside said indicator housing, said blown fuse indicator including a pair of coaxial complementary indicator caps biased in opposite directions by a helical spring arranged inside said pair of indicator caps, and means for securing one of said pair of indicator caps to the end of said blown fuse indicator restraining wire extending across said end surface of said one of said pair of terminal caps.

2. An electric fuse as specified in claim 1 wherein said ribbon fuse link is planar and is arranged in a plane including the axis of said casing, and wherein said blown fuse indicator restraining wire is arranged substantially in the same plane as said ribbon fuse link and sufficiently close to said ribbon fuse link to be severed by the electronic are formed incident to interruption of said ribbon fuse link.

3. An electric cartridge fuse including a. a tubular casing of insulating material;

b. a pair of terminal caps mounted on the ends of said casing and closing the ends thereof;

c. a ribbon fuse link conductively interconnecting said pair of terminal caps; v

d. a pulverulent arc-quenching filler inside said casing embedding said ribbon fuse link;

. a blown fuse indicator restraining wire extending across the end surface of one of said pair of terminal caps to the outside of said casing;

f. a tubular blown fuse indicator housing arranged in coaxial relation to said casing and defining a shoulder abutting against said end surface of said one of said pair of terminal caps, said blown fuse indicator housing further having a sleeve-like extension engaging and overlapping the lateral surface of said one of said pair of terminal caps and affixed to said one of said pair of terminal caps; and

g. a blown fuse indicator inside said indicator housing, said blown fuse indicator including a normally recessed indicating element, a helical spring biasing said indicating element in a direction longitudinally of said casing and of said indicator housing, a support for the end of said spring remote from said indicating element, and means arranged inside said indicator housing for securing said indicating element to one end of said blown fuse indicator restraining wire. l 

1. An electric fuse including a. a tubular casing of insulating material; b. a pair of terminal caps mounted on the ends of said casing and closing the ends thereof; c. a ribbon fuse link conductively interconnecting said pair of terminal caps; d. a pulverulent arc-quenching filler inside said casing embedding said ribbon fuse link; e. a blown fuse indicator restraining wire extending across the end surface of one of said pair of terminal caps to the outside of said casing; f. a tubular blown fuse indicator housing arranged in coaxial relation to said casing and defining a shoulder abutting against said end surface of said one of said pair of terminal caps, said blown fuse indicator housing further having a sleeve-like extension engaging and overlapping the lateral surface of said one of said pair of terminal caps and affixed to said one of said pair of terminal caps; and g. a blown fuse indicator inside said indicator housing, said blown fuse indicator including a pair of coaxial complementary indicator caps biased in opposite directions by a helical spring arranged inside said pair of indicator caps, and means for securing one of said pair of indicator caps to the end of said blown fuse indicator restraining wire extending across said end surface of said one of said pair of terminal caps.
 2. An electric fuse as specified in claim 1 wherein said ribbon fuse link is planar and is arranged in a plane including the axis of said casing, and wherein said blown fuse indicator restraining wire is arranged substantially in the same plane as said ribbon fuse link and sufficiently close to said ribbon fuse link to be severed by the electronic arc formed incident to interruption of said ribbon fuse link.
 3. An electric cartridge fuse including a. a tubular casing of insulating material; b. a pair of terminal caps mounted on the ends of said casing and closing the ends thereof; c. a ribbon fuse link conductively interconnecting said pair of terminal caps; d. a pulverulent arc-quenching filler inside said casing embedding said ribbon fuse link; e. a blown fuse indicator restraining wire extending across the end surface of one of said pair of terminal caps to the outside of said casing; f. a tubular blown fuse indicator housing arranged in coaxial relation to said casing and defining a shoulder abutting against said end surface of said one of said pair of terminal caps, said blown fuse indicator housing further having a sleeve-like extension engaging and overlapping the lateral surface of said one of said pair of terminal caps and affixed to said one of said pair of terminal caps; and g. a blown fuse indicator inside said indicator housing, said blown fuse indicator including a normally recessed indicating element, a helical spring biasing said indicating element in a direction longitudinally of said casing and of said indicator housing, a support for the end of said spring remote from said indicating element, and means arranged inside said indicator housing for securing said indicating element to one end of said blown fuse indicator restraining wire. 